SEQUENTIAL CYCLIZATION SILYLATION OF ENYNES CATALYZED BY AN ORGANOYTTRIUM COMPLEX/

The organoyttrium complex Cp2YCH3.THF (Cp* = C5Me5) has been shown to be an effective precatalyst for the selective sequential cyclization/ silylation of 1,6- and 1,7-enynes.. The catalyst's ability to insert t he alkyne in preference to the alkene in a regioselective manner, comb ined with the high diastereoselectivity of the insertion process, yiel ds a product with only one stereochemistry about the exocyclic olefin. The reaction proceeds under extremely mild conditions with short reac tion times. Cyclization of enynes functionalized in the allylic positi on affords silylated carbocycles with high diastereoselectivities and excellent yields.